The present invention relates generally to a hydraulic system, and more particularly to a hydraulic system with an air-venting arrangement.
It is hardly necessary to emphasize that the proper operation of hydraulic systems is most disadvantageously influenced if air is permitted to enter and remain in the hydraulic circuit. Of course, the entry of air into such a circuit is often unavoidable. In such a circumstance, however, it is most important that the air which has entered be vented. The various types of pumps used for moving the hydraulic fluid in the circuit, for instance gear pumps or the like, are not able -- due to the gaps between the pump housing and the impellers used -- to so compress the entrapped air that it can overcome the closing pressure of a one-way valve incorporated in the circuit or to actuate the user; the result, if the air is allowed to remain, would be that after a short period of time the pump would become inoperative.
Of course, the problem of venting entrapped air from a hydraulic system is not new and attempts have been made to provide appropriate arrangements for this purpose. It is frequently customary to provide at an appropriate point of the hydraulic circuit a venting screw which is loosened when venting is to take place, for instance when the pump for the hydraulic fluid is first started up. After the pump has been operated briefly and it is certain that the entrapped air has been expelled from the circuit by the advancing hydraulic fluid, the screw is tightened again. This is a quite effective and reliable manner of venting a hydraulic system, but evidently it is also a time consuming and rather cumbersome procedure, especially when it is considered that the procedure must be repeated each and every time air has entered the system, for instance each and every time the pump is started up after having been stopped.
A somewhat improved arrangement known from the art utilizes a venting valve which is so accommodated in a hydraulic system that entrapped air can enter into a chamber of a valve housing. A differential-pressure slide is accommodated in the chamber and, when the pressure increases in the system, the slide is displaced so that it closes the chamber and compresses the air which has been trapped therein. In a certain position the slide opens a passage through which the entrapped air can then vent to the atmosphere. When the pressure in the system decreases, the slide returns to its starting position.
This arrangement, also, is possessed of disadvantages of which the most important is the fact that when a larger quantity of air is to be allowed to escape, it is necessary to mechanically push the slide inwardly into the housing (after first removing a protective cap) until the air has been displaced by the advancing hydraulic fluid. Evidently, this is a relatively complicated construction and also time consuming operation, so that this proposal still is far from satisfactory.